A popular, though somewhat disputed hypothesis is that patients allergic asthma and certain other respiratory tract diseases that are characterized by hyperresponsive airways, exhibit exaggerated adverse bronchomotor responses primarily because of some anomaly in the parasympathetic reflex control of airway caliber. The nature of the neural mechanisms mediating these abnormal reflexes has not been elaborated. The overall goal of this project is to identify the anomaly within the parasympathetic nervous system that could lead to airway hyperreactivity. Successful identification could result in the development of a more enlightened treatment of patients with this specific problem than is currently available. In order to achieve this goal, experiments will be done in anesthetized dogs as follows. Reflexly-mediated changes in the bronchomotor tone of a tracheal segment, isolated in situ fromboth the arterial blood supply of the animal and the rest of the respiratory tract and lungs, will be monitored. These changes will be evoked by a variety of known reflexogenic chemical and mechanical manipulations of the lungs. Before, during, and after these maneuvers sensory neurograms from the lungs and efferent nerve traffic tothe isolated segment will be monitored simultaneously along with the bronchomotor changes. Quantitative relationships will be established: 1) between the activity of each of the different types of sensory modalities known to be present in the lungs and the efferent discharge to the segment; 20 between each type of sensory discharge and the magnitude of the change in bronchomotor tone; and 30 between the efferent discharge to the segment and the magnitude of the change in bronchomotor tone. These relationships will be examined within a wide range of arterial blood gas changes in both normal dogs and those with hyperractive or asthmatic airways. These data will provide unique information about the interactions that occur among the different components that make up a reflex bronchomotor pathway in both normal and asthmatic or hyperresponsive dogs. In addition, a comparison of the relatinships in normal dogs to those in dogs with hyerresponsive or asthmatic airways could reveal differences which could account for the exaggerated responses inthe latter two groups.